For storing, transporting and bringing into practical use of materials susceptible to denaturing, such as living organisms, organic materials, foods, drugs, biological samples, feeds and industrial raw materials, they are often processed into a frozen or freeze-dried product. For example, for analyzing a biological material, a sample is prepared by a series of operations for processing the material, such as freezing, drying, crushing and homogenizing.
Freezing may generally be realized using a refrigerator. Here, it takes a relatively prolonged period of time till the freezing temperature is reached, during which the material to be processed may suffer from denaturation due to the presence of oxygen and/or enzymes. Even after the freezing has been completed the, stability during storage may not always be satisfactory because of the presence of oxygen.
Freeze-drying may often be practiced after the material to be processed has preliminarily been treated by crushing and homogenization. Such a crushing operation may cause a temperature elevation of the material due to heat evolution upon crushing. The material may suffer from denaturing due to such a temperature elevation in combination with the presence of oxygen, so that the procedures of crushing, homogenization and freezing are not able to realize the preservation of the original quality and condition of the material.
For eliminating such difficulties, it has been in practised to cool the crusher and homogenizer or, in addition, to exclude any contact of the material under treatment with oxygen. However, such countermeasures require large and complicated arrangements and, were not satisfactory for the contemplated prevention of denaturing of the treated material due to inefficiency of cooling and lack of oxygen elimination.
This has been shown, as widely been recognized in the commercial field of, for example, dry foods, such as dried vegetables etc., convenience foods and the like, by the fact that the taste, color and material condition of such treated articles are debased or deteriorated, resulting in a decrease in the merchandise value and, in the case of the analysis of a sample, biasing the analytical results. Some food products, in particular, vegetables may be pretreated by so-called blunting for deactivation of the enzymes therein by heat treatment before being frozen, wherein, however, denaturing may often occur.